So-called roll or roll-up type doors are widely used in industrial applications to close off sections of industrial buildings or to seal a doorway which opens to the exterior of the building. Such doors are typically characterized by a flexible, fabric curtain type closure member supported on a rotatable shaft wherein the side edges of the closure member are disposed in opposed guideways on opposite sides of the doorway and the door is controlled for rapid opening and closing action. Since such doors are often used in facilities wherein there is a substantial amount of traffic through the doorway, releasable or so-called breakaway connections have been developed to permit the door closure member to be released from the guideways if struck by a vehicle traversing the doorway to prevent or reduce damage to the door, the vehicle or injury to personnel exposed to such incidents. Other features which have been considered desirable for roll-up doors include a support frame which reduces the space occupied along each side of the doorway, ease of erection and assembly of the door at the site and a door actuating mechanism which does not exert the full force or torque of the drive motor on the door bottom edge, in the event that an object is in the doorway when the door moves to a closed position.
There have been several developments in breakaway connection devices between opposed sides of a roll-up door at the bottom edge and the door guideways. Many of these connection devices are relatively complex and require a substantial amount of time to reconnect the door to the guideways and the door actuating mechanism if the breakaway connection is released. Prior art door breakaway connections include types wherein a pivoting latch member is held in position by a detent member and pivots or releases from the detent to permit operation of the breakaway connection. Other types of breakaway connections include frangible pin type connections which must be replaced once the breakaway connection has actuated.
Roll-up type doors are also typically adapted to be actuated in such a way that the door closure member is always under tension in order to keep the flexible fabric in a relatively stiff operating condition to provide proper functioning of the door. Relatively complex cable and travelling weight mechanisms have been developed for tensioning the door and counterbalancing the weight of the door. Somewhat complicated counterbalance spring arrangements have been developed which are disposed within the door roll support shaft or drum.
Accordingly, there has been a need to develop a breakaway connection which is mechanically uncomplicated, reliable in operation and provides for relatively easy reconnection of the door bottom bar or bottom edge to the door traversing mechanism and guideway. There has also been a need to improve the door side edge seals to provide for a substantially weather-tight seal at the doorway. Still further, a need has existed for improvements in the mechanism which provides for tensioning the door bottom edge under all operating conditions. The present invention provides solutions to the above-mentioned problems associated with roll-up doors as well as providing other advances in the art of such doors.